Welcome to the Ranch.
You probably have a problem with the character encoding. The first thing you have to do is find out where it goes wrong. Is the data stored in the database correctly? If not, then it is somewhere between submitting the text and storing it in the database. If it is correct in the database, then is it being read correctly from the database? And is it being sent to the client correctly?
Is this a web application, where the text is displayed in a browser? Is the character encoding set correctly in the HTML page?
What does "it can't show bangla" mean exactly - do you get squares or question marks or strange characters on screen, or do you get an error message or does something else happen?
Note that you have to be careful, this kind of problem can be tricky to debug. For example, some tools cannot display foreign language characters correctly, so it could happen that you're looking in the database to see if the text is correct there, but that the tool you're using to look into the database is unable to display the characters.
If you want to know more about character sets and encodings, then
this article gives a good overview.